The smart way to improve grades

Comprehensive & curriculum aligned

Affordable pricing from £10/month

The Atmosphere

Worksheet Overview

QUESTION 1 of 10

This activity is about the air around us; what it's like now, and what it was like in the past.

It would be really cool to find this out by going in a time machine, but they don't exist. Fortunately, scientists can use evidence and thinking to work out what the Earth's atmosphere was like in the past, and compare it with what we have now.

As you think about this topic, notice how scientists can get evidence for the past from surprising sources.

Earth's atmosphere today

This pie chart shows the composition of the atmosphere today;

About four-fifths of the gas in the atmosphere is nitrogen. About one-fifth is oxygen. There is a small amount (about 1 %) of argon, and a very small amount (about 0.04 %) of carbon dioxide. Although the proportion of carbon dioxide is tiny, there is still enough carbon dioxide to have important effects on the Earth's environment.

Earth's atmosphere in the past

The outline story of the Earth's atmosphere is something like this;

How long ago? What happened? How did this affect the atmosphere?
4.6 billion years ago Earth formed, volcanoes started erupting The atmosphere was full of carbon dioxide, with some water vapour 
3.8 billion years ago Earth cooled enough for liquid water to condense Water went from the atmosphere into oceans, some carbon dioxide dissolved in the oceans as well
2.7 billion years ago Algae appeared, and started to photosynthesise Carbon dioxide was removed from the atmosphere. Initially the oxygen produced mainly went into rocks.
2.2 billion years ago Rocks could take no more oxygen Oxygen levels in the atmosphere began to increase, until there was almost no carbon dioxide in the atmosphere.

Let's start at the beginning, when the Earth first formed. Almost no rocks from that time exist on Earth, so we have to be very ingenious when looking for evidence.

What was Earth's original atmosphere like, and what evidence do we have?

The planet Venus is like the Earth in some ways, but its atmosphere is very different. The atmosphere on Venus is nearly all carbon dioxide, with a small amount of nitrogen. Scientists think that Earth's atmosphere when it first formed (about 4.6 billion years ago) was like this, with lots of carbon dioxide and water vapour which had escaped from volcanoes. One reason we think this happened on Earth is by studying volcanoes which erupt today, and observing the gases they give off.

How did the formation of oceans affect the atmosphere, and what evidence do we have?

Gradually, the Earth cooled down. About 3.8 billion years ago, it got cool enough for water vapour in the atmosphere to condense and make liquid water, which collected in oceans. A lot of the original carbon dioxide went from the atmosphere to the oceans. The big clue that there was liquid water on the Earth's surface at this time is that the oldest sedimentary rocks are about 3.8 billion years old. Without water, sedimentary rocks can't form. Some of these rocks contain carbonate minerals, and we know from the modern carbon cycle that the formation of carbonate rocks removes carbon dioxide from the atmosphere.

How did the appearance of algae affect the atmosphere, and what evidence do we have?

The next big change was the appearance of algae on planet Earth, about 3.5 billion years ago. Algae are small green organisms. They look like plants, but their cells are organised differently. You often see them floating on the top of ponds, like this;

Green plants gradually converted nearly all the carbon dioxide in the Earth's atmosphere to oxygen, by photosynthesis;

carbon dioxide + water → glucose + oxygen.

We know when algae evolved from the fossil record; we can see fossil algae in rocks up to 3.5 billion years old, but not in older rocks. We know their effect by observing modern algae.

Why didn't oxygen levels increase straight away?

Some of the oxygen produced ended up in rocks (think things like iron oxide), but eventually oxygen gas collected in the atmosphere as well. That eventually gave us the atmosphere we have now. The clue that this happened is a type of rock called the banded iron formation;

These rocks formed in lots of places around the world, but only about 2 billion years ago. The red bands are iron oxide, which carried away the oxygen produced by algae. Once all the available iron had been oxidised, while silica was deposited instead. These two types of rock alternated until there was nothing left to oxidise; after that, oxygen collected in the atmosphere.

Another piece of evidence is the way that plant fossils have changed over time. Plant leaves have holes (called stomata) where carbon dioxide can enter the leaf for photosynthesis. Ancient leaf fossils have many fewer stomata than modern plants. We think this is because there used to be more carbon dioxide in the atmosphere, so it was easier for plants to collect the carbon dioxide they needed. As carbon dioxide levels have fallen, plants have needed more stomata.

That's the outline of the story. Scientists aren't exactly sure about the precise dates, or some of the details, but this outline is consistent with a lot of things we see around us. Without a time machine (and nobody knows how to make one of those), it's the best we can do.

 

What is the proportion of each of these gases in the Earth's atmosphere today? Give each of your answers to the nearest whole percent.

Where did the original atmosphere for Venus and Earth come from?

the Sun

outer space

volcanoes

plants

When did oceans form on the Earth, and how do we know?

the Sun

outer space

volcanoes

plants

Some of the 3.8 billion year old rocks were carbonates. What does that tell us?

There was oxygen in the atmosphere

There was nitrogen in the atmosphere

The ancient oceans contained some carbon dioxide

All carbon dioxide disappeared from the atmosphere

When did each of these changes happen to the atmosphere?

There was oxygen in the atmosphere

There was nitrogen in the atmosphere

The ancient oceans contained some carbon dioxide

All carbon dioxide disappeared from the atmosphere

How do we know when algae evolved, and why does this matter?

There was oxygen in the atmosphere

There was nitrogen in the atmosphere

The ancient oceans contained some carbon dioxide

All carbon dioxide disappeared from the atmosphere

This type of rock is called the banded iron formation;

Why does it help us understand the history of Earth's atmosphere?

The red layers absorbed oxygen

The red layers gave off oxygen

The red layers are fossils of algae

What are the air holes on the underside of leaves called?

How are stomata in ancient leaf fossils different to stomata in modern leaves? What does this tell us about the atmosphere?

What is the main gas in the atmosphere of Venus?

  • Question 1

What is the proportion of each of these gases in the Earth's atmosphere today? Give each of your answers to the nearest whole percent.

CORRECT ANSWER
EDDIE SAYS
The amount of carbon dioxide is 0.04 %, which rounds to 0 %. Although the amount is tiny, it still has a significant effect on the planet.
  • Question 2

Where did the original atmosphere for Venus and Earth come from?

CORRECT ANSWER
volcanoes
EDDIE SAYS
Venus and Earth are both made of similar materials, and the surface of Venus has many extinct volcanoes. We know that volcanoes on Earth give off carbon dioxide today, which is why we think that was where the original atmosphere for Venus and Earth came from volcanoes.
  • Question 3

When did oceans form on the Earth, and how do we know?

CORRECT ANSWER
EDDIE SAYS
We can't make sedimentary rocks without liquid water, so knowing when sedimentary rocks started to be made tells us when liquid water was first present. It's one of the things scientists are looking for on Mars, to see if liquid water was ever present on that planet.
  • Question 4

Some of the 3.8 billion year old rocks were carbonates. What does that tell us?

CORRECT ANSWER
The ancient oceans contained some carbon dioxide
EDDIE SAYS
Some of the carbon dioxide from the atmosphere ended up dissolved in the oceans, and forming carbonate rocks. Not all of it though- there was still quite a lot in the atmosphere.
  • Question 5

When did each of these changes happen to the atmosphere?

CORRECT ANSWER
EDDIE SAYS
The sequence is much more important than the exact dates (though you should learn them if you can!). Find ways of memorising sequences like this which work for your brain; it might be a flow chart, or a sequence of cartoon images, or a mnemonic.
  • Question 6

How do we know when algae evolved, and why does this matter?

CORRECT ANSWER
EDDIE SAYS
The fossil record lets us see when organisms first appeared, or became extinct. The effect of algae is to remove carbon dioxide from the atmosphere; there's evidence that this reduced the temperature of the planet.
  • Question 7

This type of rock is called the banded iron formation;

Why does it help us understand the history of Earth's atmosphere?

CORRECT ANSWER
The red layers absorbed oxygen
EDDIE SAYS
The red layers are iron oxides, a bit like rust. This absorbed oxygen produced by algae, so it didn't go into the atmosphere for a long time. Only once rocks were fully oxidised could oxygen gas collect in the atmosphere.
  • Question 8

What are the air holes on the underside of leaves called?

CORRECT ANSWER
stomata
stoma
EDDIE SAYS
You will learn more about leaf structure in biology. It's one stoma, more than one stomata.
  • Question 9

How are stomata in ancient leaf fossils different to stomata in modern leaves? What does this tell us about the atmosphere?

CORRECT ANSWER
EDDIE SAYS
If there's more carbon dioxide in the air, it's easier for a plant to collect the carbon dioxide it needs, so it will have fewer stomata. Stomata are a problem for plants, because they lose water through them, so they try to have and open as few as possible.
  • Question 10

What is the main gas in the atmosphere of Venus?

CORRECT ANSWER
carbon dioxide
EDDIE SAYS
The same is true on Mars (though most of Mars\'s atmosphere has escaped into space). That\'s a good clue that Earth\'s atmosphere was originally carbon dioxide. The interesting (and partly unsolved) question is- what was different about Earth that it didn\'t stay this way?
---- OR ----

Sign up for a £1 trial so you can track and measure your child's progress on this activity.

What is EdPlace?

We're your National Curriculum aligned online education content provider helping each child succeed in English, maths and science from year 1 to GCSE. With an EdPlace account you’ll be able to track and measure progress, helping each child achieve their best. We build confidence and attainment by personalising each child’s learning at a level that suits them.

Get started
laptop

Start your £1 trial today.
Subscribe from £10/month.